The timing cover of this Mazda 2 and 3 under the ZJ engine code, have a very special o-ring at the timing cover which we mark at the above timing cover photo, and we can't find this o-ring is included in the overhaul set gasket kit. Since it is not in the engine overhaul gasket kit set, it may be include in their timing chain kit set but I'm not sure if it is or their timing chain replacement is done by purchasing all individual items.
Anyway, Mazda did service this o-ring for replacement in case the car owner just need to replaced that o-ring, under OEM part number ZJ01-10-673B, you may find this o-ring design quite interesting in the photo below.
